This invention relates generally to polymer compositions useful in photoresist compositions. In particular, this invention relates to polymer compositions including spirocyclic olefin units useful as binders in photoresist compositions.
Photoresists are photosensitive films used for transfer of images to a substrate. A coating layer of a photoresist is formed on a substrate and the photoresist layer is then exposed through a photomask to a source of activating radiation. The photomask has areas that are opaque to activating radiation and other areas that are transparent to activating radiation. Exposure to activating radiation provides a photoinduced chemical transformation of the photoresist coating to thereby transfer the pattern of the photomask to the photoresist-coated substrate. Following exposure, the photoresist is developed to provide a relief image that permits selective processing of a substrate.
A photoresist can be either positive-acting or negative-acting. For most negative-acting photoresists, those coating layer portions that are exposed to activating radiation polymerize or crosslink in a reaction between a photoactive compound and polymerizable agents of the photoresist composition. Consequently, the exposed coating portions are rendered less soluble in a developer solution than unexposed portions. For positive-acting photoresists, exposed portions are rendered more soluble in a developer solution while areas not exposed remain comparatively less developer soluble. In general, photoresist compositions include at least a resin binder component and a photoactive agent.
More recently, chemically-amplified type resists have been increasingly employed, particularly for formation of sub-micron images and other high performance applications. Such photoresists may be negative-acting or positive-acting and generally include many crosslinking events (in the case of a negative-acting resist) or deprotection reactions (in the case of a positive-acting resist) per unit of photogenerated acid. In the case of positive chemically-amplified resists, certain cationic photoinitiators have been used to induce cleavage of certain “blocking” groups pendant from a photoresist binder, or cleavage of certain groups comprising a photoresist binder backbone. See, for example, U.S. Pat. Nos. 5,075,199; 4,968,581; 4,810,613; and 4,491,628 and Canadian Patent Application 2,001,384. Upon cleavage of the blocking group through exposure of a coating layer of such a resist, a polar functional group is formed, e.g. carboxyl or imide, which results in different solubility characteristics in exposed and unexposed areas of the resist coating layer. See also R. D. Allen et al. Proceedings of SPIE, 2724:334–343 (1996); and P. Trefonas et al. Proceedings of the 11th International Conference on Photopolymers (Soc. of Plastics Engineers), pp 44–58 (Oct. 6, 1997).
While currently available photoresists are suitable for many applications, current resists can also exhibit significant shortcomings, particularly in high performance applications such as formation of highly resolved sub-half micron and sub-quarter micron features.
Consequently, interest has increased in photoresists that can be photoimaged with short wavelength radiation, including exposure radiation of about 250 nm or less, or even about 200 nm or less, such as wavelengths of about 248 nm (provided by a KrF laser) or 193 nm (provided by an ArF exposure tool). Use of such short exposure wavelengths can enable formation of smaller features. Accordingly, a photoresist that yields well-resolved images upon 248 or 193 nm exposure could enable formation of extremely small (e.g. sub-quarter micron) features that respond to constant industry demands for smaller dimension circuit patterns, e.g. to provide greater circuit density and enhanced device performance.
However, many current photoresists are generally designed for imaging at relatively higher wavelengths, such as I-line (365 nm) and G-line (436 nm) exposures, and are generally unsuitable for imaging at short wavelengths, such as 248 nm and 193 nm. In particular, prior resists exhibit poor resolution (if any image at all can be developed) upon exposure to these shorter wavelengths. Among other things, current photoresists can be highly opaque to extremely short exposure wavelengths, such as 248 nm and 193 nm, thereby resulting in poorly resolved images. Efforts to enhance transparency for short wavelength exposure can negatively impact other important performance properties such as substrate adhesion or swelling, which in turn can dramatically compromise image resolution.
Cyclic monomer units, particularly those containing functional groups, impart various properties to the resin binder when incorporated into the backbone of the resin binder. Anhydrides incorporated into the resin binder backbone help reduce swelling. For example, Barclay et al., The Effect of polymer Architecture on the Aqueous Base development of Photoresists, Polym. Prepr. (American Chemical Society, Division of Polymer Chemistry), volume 40(1), pages 438–439, 1999, discloses the incorporation of itaconic anhydride into a photoresist resin binder, such as a (meth)acrylic polymer. However, such anhydrides can undergo hydrolysis in the presence of alcohols or other solvents, especially solvents that are contaminated with small amounts of water.
Such swelling of resin binders could be even further reduced or eliminated through the use of a binder containing a high proportion of cyclic monomers in the polymer backbone, particularly cyclic monomers containing functional groups. One approach for achieving this is to use only cyclic monomers in the preparation of the polymer. However, this approach suffers from the difficulty in polymerizing such cyclic monomers, especially when the cyclic monomers contain electron withdrawing groups, such as anhydrides. In particular, 5-norbornene-2,3-dicarboxylic anhydride cannot be easily polymerized.
For example, WO 99/42510 discloses resins useful in photoresist compositions wherein the resin is composed of norbornyl monomers containing various functional groups. This patent application is directed to a method for preparing a polycyclic polymer and introducing difficult to polymerize functionalities into the polymer by post-polymerization functionalization. Such post polymerization treatment avoids the use of monomers containing such difficult to polymerize functionalities as nitrogen containing groups, such as amides, and hydroxyl containing groups, such as alcohols and carboxylic acids. The post polymerization functionalization is achieved by using cyclic monomers containing protected functionalities, deprotecting the functionality to give a free functionality and then reacting the free functionality to give a post-functionalized moiety. Drawbacks of this invention are that the mass of the polymer resin may change, resulting in shrinkage of the polymer, and a number of extra steps are required which greatly adds to the time and cost of the preparation.
Polymers containing tricyclic nornornenyl monomers composed of a norbornyl ring fused to a 5-membered anhydride ring are disclosed in WO 99/42510. However, spirocyclic monomers are not disclosed in that patent application.
Japanese Patent Application JP 10 310 640 A, to Maruzen Petrochem Co. Ltd., discloses a variety of spirocyclic olefin monomers including those containing lactone and imide functional groups. Spiropolyimides are also disclosed, however, such polyimides are bound to the polymer backbone through the imide nitrogen groups. This patent application does not disclose spirocyclic monomer units bound to the polymer backbone through the olefinic carbons of the spirocyclic olefin monomers.
It is thus desirable to have photoresist compositions that can be imaged at short wavelengths, contain resin binders having reduced swelling and have better substrate adhesion than known photoresist compositions. It is further desirable to have photoresist compositions containing resin binders that have mass persistence and can be prepared with few reactions or transformations.